Deep inside the trenches of the Southern Ocean, Australian researchers have discovered for the first time the ongoing impact of ocean currents on the distribution and abundance of critical marine micro-organisms.

By collecting samples taken more than six kilometers under the surface of one of the world's more fickle oceans, the sampling by researchers at the University of New South Wales(US), was the deepest of its kind ever undertaken, according to the information from US on Wednesday.

From the rugged Australian icebreaker, RSV Aurora Australis, Professor Rick Cavicchioli, of the US School of Biotechnology and Biomolecular Sciences, and team leader has sought answers to the critical questions surrounding the life-cycle of ocean- microbes.

Microbes are the foundation of the ecological pyramid that determines the health of not only the ocean but all life within it.

According to Cavicchioli the microbes are invisible to the naked eye, and vital to sustaining life on earth, producing most of the oxygen we breathe, soaking up carbon dioxide from the atmosphere and recycling nutrients.

"Microbes form the bulk of the biomass in oceans. All the fish, dolphins, whales, sponges and other creatures account for less than 5 percent of the biomass," says Professor Cavicchioli.

"Microbes perform roles that nothing else can carry out. And if one critical group of microbes was destroyed, life on the planet would cease to exist."

The influence of environmental conditions on the make-up of microbial communities in different regions of the ocean has been studied, as has the role of physical barriers in preventing their dispersal.

"Collecting samples in the Southern Ocean was an enormous challenge. But it has meant we were able to carry out the first study showing how physical transport in the ocean on currents can also shape microbial communities," says Professor Cavicchioli.

What makes the research so critical are the huge numbers of microbes within the open ocean.

Coastal areas around the world can contain even greater concentrations of bacteria and plankton occurring both at the surface and in deep ocean waters.

Previous scientific studies indicate that 10 to 100 million viruses can be present in a teaspoonful of sea water.

Most important of the microbes now pumping through the world's oceans like blood trough the human body, are the phytoplankton harvesting the energy of the sun and converting it into tissues which form the basis of the food chain in the ocean.

All ocean life depends on phytoplankton either directly or indirectly and it is the previously un-examined plankton superhighways that form the basis of the latest US research, the results of which have been published in the journal Nature Communications.

Twenty-five samples were collected across a 3,000 kilometer stretch of ocean between Antarctica and the southern tip of Western Australia. Sampling depths were determined by temperature, salinity and dissolved oxygen measurements, to ensure microbes were collected from all the distinct water masses of the Southern Ocean.

These water masses include the circumpolar deep water, which flows toward the south pole from the Indian, Pacific Ocean and Atlantic oceans; the surface water near the Antarctic coastline; and the cold, dense Antarctic bottom water, which flows north, away from the pole, at more than 4 kilometers' depth.

Genetic sequencing of the microbial DNA in each sample was carried out to characterize the microbial communities in different water-masses. The research shows that communities that are connected by ocean currents are more similar to each other.

"So a microbial community could be very different to one only a few hundred meters away, but closely related to one that is thousands of kilometers away because they are connected by a current," says Professor Cavicchioli.

"Researchers need to take this into account when they are studying these important micro-organisms."

The results were tested by Dr Erik Van Sebille, of the US Climate Change Research Center, who used a computer model of the Southern Ocean to carry out a 100-year long simulation of how particles would move as a result of ocean circulation.

Dr. David Wilkins, who carried out the research under Professor Cavicchioli's supervision, is the first author on the paper. The team also included US's Dr. Federico Lauro and Dr. Stephen Rintoul, of the Australian science organization, the CSIRO.